1. Field of the Invention
The present invention relates to an apparatus for drawing a conductor print pattern of defogging heater wires on a motor vehicle window.
2. Description of the Prior Art
Defogging heater wires on a motor vehicle glass window are formed by screen printing and sintering of conductive paste.
A known process is used for screen printing. Generally, a developed plan view (two-dimensional drawing) of a glass material is produced from a plan (trihedral views) of a glass window. A conductor pattern drawing is produced on the developed view on the basis of given specifications such as a conductor width and a distance between the conductors etc. of heater wires in a one-to-one size. A peeling film is cut along an outline of the conductor pattern to produce a cut mask in which conductor portion remains uncut. The cut mask is adhered to a screen on which a photosensitive material is applied. The resultant cut mask is exposed and washed with water to prepare a print screen in which a conductor portion corresponds to an opening. The screen overlaps the glass plate to print the conductive paste.
A width of each conductor is limited to be 1 mm or less so as not to interfere the field of view. In addition, the lengths of a large number of heater wires formed between bus bars are different from each other, so that the widths of the respective conductors are changed so as to equally set resistances of the wires. Furthermore, in order to differentiate a heating power (resistance) of a central portion (high-temperature area) from that of peripheral portions (low-temperature areas), conductor width of each heater wire must be modified in every heating area.
For this reason, drawing of a conductor pattern and preparation of a cut mask are performed by extremely sophisticated and precise manual operations. These operations are time-consuming even by a skilled person.
When various types of products are manufactured in small quantities, the above manual operations are obstacles for reducing cost and simplifying the manufacturing process.